The present invention relates to an antenna device mainly used in wireless unit for mobile communication or the like, and a method of manufacturing the same.
Recently there is a rapidly increasing demand for wireless unit for mobile communication such as cellular phone. The wireless unit is diversified in function so as to transmit and receive more information by one unit. To meet such demand for multiple functions, a wireless unit capable of transmitting and receiving radio waves in plural frequency bands is developed. To cope with plural frequencies, the wireless unit has an antenna setting two or more impedance characteristics.
As the antenna applicable to plural frequency bands, the helical antenna with coil winding is widely used.
A conventional antenna is explained by referring to FIG. 28.
FIG. 28 is a sectional view of a conventional antenna device applicable to two frequency bands. As shown in FIG. 28, a conventional antenna device 6 comprises:
a) a first helical antenna element (HAE) 1 made of copper wire or copper alloy wire,
b) a second HAE 4 made of copper wire or copper alloy wire,
c) a core 3 made of insulating resin for winding the HAE 1 and HAE 4 while insulating the HAE 1 and HAE 4,
d) a mounting bracket 2 made of metal for mounting the core 3 on which the HAE 1 and HAE 4 are wound, and further mounting on the wireless unit, and
e) an insulating cover 5 for covering the outer circumference of the HAE 1, HAE 4, and core 3.
The HAE 1 includes an upward coil winding 1A, and a junction 1B for electrically connecting to the mounting bracket 2. The mounting bracket 2 has a circular recess 2A for fitting the lower end of the core 3. The winding 1A of the HAE 1 is wound around the core 3 which is fixed to the recess 2A. The junction 1B at the lower end of the HAE 1 is electrically connected to the recess 2A of the mounting bracket 2. The winding diameter and winding pitch of the HAE 1 are same as the winding diameter and winding pitch of the HAE 4. In the winding pitch of the winding 1A of the HAE 1, the HAE 4 is wound. As a result, the HAE 1 and HAE 4 are mutually insulated. The HAE 4 is parasitic, and is insulated from the mounting bracket 2. An insulating cover 5 is formed by insert molding of insulating resin on the outer circumference of the core 3 on which the HAE 1 and HAE 4 are wound.
In the antenna device 6 thus composed, when sending and receiving radio waves, an electric current is induced between the windings of the HAE 1 and HAE 4 by electromagnetic inductive action. Making use of the induced current, the wireless unit having the antenna 6 can send and receive radio waves in at least two frequency bands.
The configuration of the HAE 1 and parasitic HA 4 requires high precision so as not to contact with each other and to maintain the desired antenna characteristic. In the conventional antenna 6, however, the winding may be uneven in pitch or may be deformed when winding the copper wire or copper alloy wire on the core 3 and covering with the insulating resin 5. Therefore, in the conventional antenna device having such structure, it is hard to obtain an impedance characteristic corresponding to a desired frequency band. That is, in the gain of the conventional antenna device, fluctuations were large. Accordingly, in order to obtain an antenna having a desired characteristic, it was necessary to sort out. There was also a limit for enhancing the yield of the conventional antenna device. In the conventional antenna device, therefore, reduction of cost was limited by the sorting process and the yield.
The invention relates to an antenna device having two or more impedance characteristics capable of solving the problems of the conventional antenna device. It is hence an object of the invention to present an antenna device hardly causing uneven pitch or deformation of antenna elements, stable in gain, and high in reliability. It is also an object of the invention to present a method of manufacturing antenna devices excellent in productivity.
To achieve the object, the antenna device of the invention comprises:
a) a first antenna element (FAE) of spiral form having nearly parallel plural bands formed so that both ends may be connected alternately and consecutively, and formed so that at least one or more bands may be projected,
b) a second antenna element (SAE) of meandering form having nearly parallel plural bands formed so that both ends may be connected alternately and consecutively, and formed so that at least one or more bands may be projected,
c) a core made of an insulating resin for disposing the FAE and SAE nearly at concentrical positions,
d) a mounting bracket connected to one end of the FAE, and
e) a cover made of an insulating resin for covering the outer circumference of each member, by exposing a part of the mounting bracket.
The FAE and SAE are formed by pressing a conductive thin metal plate punched in a specified shape into a desired shape. In order that the FAE and SAE may be mutually insulated, each inner side is fixed to the core. One end of the FAE is electrically connected to the mounting bracket. The mounting bracket has a threaded portion for mounting on a wireless unit for mobile communication such as cellular phone. The threaded portion is exposed.
Thus is presented an antenna device hardly causing uneven pitch or deformation of the antenna elements during manufacture, and having two or more impedance characteristics. It is high in reliability because uneven pitch or deformation hardly occurs.
Moreover, the antenna device having such structure can be produced easily, and the product yield is high.
The invention also provides a method of manufacturing antenna device which comprises:
a) a step of forming a first element plate by a step of punching a conductive thin metal plate of a specified dimension, and a step of pressing a part of the punched thin metal plate,
b) a step of forming a second element plate by a step of punching a conductive thin metal plate of a nearly same dimension as the first element plate, and a step of pressing a part of the punched thin metal plate,
c) a step of stacking up the outer circumferential parts of the first element plate and second element plate in the thickness direction,
d) a step of primary insert molding of a resin dielectric element for forming a core having a plurality of resin support parts by fixing the pressed portion of the stacked first element plate and the pressed portion of the second element plate,
e) a step of separating the core from the outer circumference by cutting off the flat outer circumferential parts of the pressed portion of the first element plate and the pressed portion of the second element plate near the core, and
f) a step of secondary insert molding of a resin dielectric element for forming a cover for covering the outer circumference by holding the resin support parts.
In the step of forming the first element plate of the invention,
a conductive thin metal plate of a specified dimension is blanked, and nearly parallel plural rectangular holes of same length are provided so that both ends may be convex and concave alternately, thereby forming plural linear portions,
one side of convex and concave portion of the plural rectangular holes is separated from the outer circumferential part in a linked state,
a band is formed by pressing at least a part of the linear portion of the plural linear portions,
the band is formed so as to be coupled to the outer circumference at the other side, and
a mounting bracket is connected and fixed to one end of the band, thereby forming a first element plate.
In the step of forming the second element plate of the invention,
a conductive thin metal plate is blanked, and nearly parallel plural hook holes of same length are provided alternately in reverse directions, so that plural linear portions are linked in a thin linkage alternately right and left,
one side of the plural hook holes is separated from an outer frame in a linked state,
a band is formed by pressing at least a part of linear portion of the plural linear portions, and
other side of the band is coupled to the outer circumference, thereby forming a second element plate.
In the primary insert molding step of the invention,
outer circumferential parts of the first element plate and second element plate are held,
an insulating resin is processed by insert molding,
the band of the first element plate and the band of the second element plate are fixed by resin from the inner side by this insert molding,
the mounting bracket is coupled, and
a core having a plurality of resin support parts projecting by a specified dimension from the outer circumference of the band of the first element plate and the band of the second element plate is formed.
In the step of separating the core from the outer circumference of the invention,
the core is separated from the outer circumference by cutting off near the core coupled to the outer circumference of the first element plate and second element plate, and the convex and concave linked portion at the end of the plural slots and the thin linkage are separated.
By this separation, an FAE is formed from the first element plate and an SAE is formed from the second element plate.
In the step of secondary insert molding of a resin dielectric element of the invention,
the FAE and SAE formed in the above step, and the core are molded and processed by an insulating resin, while holding the mounting bracket and the resin support parts, and
a part of the mounting bracket is exposed, and a cover for covering the outer circumference of the FAE and SAE is formed.
In the antenna device by the manufacturing method of the invention, uneven pitch or deformation of antenna elements hardly occur during manufacture, and the antenna device having two or more impedance characteristics is obtained. Moreover, since uneven pitch or deformation hardly occurs, the reliability is high.
According to the manufacturing method of the invention, the antenna device can be produced easily, and the product yield is high.
The antenna device of the invention can be used in wireless unit for mobile communication or the like, personal computer, transceiver, professional communication for example, taxi, fishing boat, police), and other wireless unit for wireless communication.